A patient under general anesthesia will undergo several physiological changes that inhibit the body's normal thermo-regulatory capabilities. General anesthesia depresses the function of thermoregulating centers in the hypothalamus, thus resulting in the body's inability to self-regulate body temperature. Infusion of intravenous fluid may contribute to cooling body temperature during surgery because such intravenous fluids absorb heat from the body when they are at a temperature below body temperature. Inspiration of dry anesthesia gases during surgery may also contribute to body temperature cooling during surgery because the dry gas both absorbs heat from the body and because of the cooling action created when water from the body is absorbed by the dry gas. Moreover, during surgery the body cavity may be exposed, which increases the effective surface area of the body and also cools body parts that are normally not exposed to the environment. The incidence of hypothermia occurring after surgery has been estimated to be as great as 60% to 90%.
To prevent hypothermia from occurring, it is necessary to provide active heating to a patient during surgery. One important requirement for any active heating system or method used during surgery is that it maintains a sterile surgical field. Another important requirement for any active heating system or method is that it delivers sufficient heat to the body to prevent the onset of hypothermia.
Although many devices exist that may be used to provide heat or to provide a sterile environment, none of these devices are capable of performing both functions simultaneously.